1. Field of the Invention
This invention relates to a process cartridge which is detachably mountable on the main body of an electrophotographic apparatus such as a color copying machine or a color printer, and also to an electrophotographic apparatus having the process cartridge, and an image-forming method making use of the electrophotographic apparatus.
2. Related Background Art
Color electrophotographic apparatus making use of an intermediate transfer member (intermediate transfer belt) conventionally have a cartridge construction in which, as disclosed in Japanese Patent Application Laid-open No. 8-137181, an electrophotographic photosensitive member unit and an intermediate transfer belt unit are independent of each other. The electrophotographic apparatus disclosed therein is so constructed that its movable-side frame can be turned around toward the front of the apparatus to open it and the electrophotographic photosensitive member unit and the intermediate transfer belt unit can each be inserted from the upper part.
On the projection upper side of the intermediate transfer belt, an electrophotographic photosensitive member unit in which a drum-shaped electrophotographic photosensitive member (photosensitive drum) and a waste-toner holder box provided on the backside are integrally supported is provided so that waste toner on the electrophotographic photosensitive member is scraped off with a cleaning blade as a cleaning means and collected in the waste-toner holder box.
Waste toner on the intermediate transfer belt is also scraped off with another cleaning blade, then transported to the lower part of a first transport pipe by means of a transport coil, and further transported by means of a screw in the first transport pipe, to the upper part at which the waste-toner holder box is provided. Thereafter, it is transported through the interior of a second transport pipe by means of a transport coil, and at length collected in the waste-toner holder box.
At a joint where the second transport pipe is joined to the waste-toner holder box, since the above electrophotographic apparatus is so constructed that the electrophotographic photosensitive member unit and the intermediate transfer belt unit are independent units and are each attached or detached, a shutter is opened or closed so that the waste toner does not spill out when they are attached or detached.
However, in the technique disclosed in the above publication, the intermediate transfer belt and the electrophotographic photosensitive member are set respectively in the different units, namely, there are two process cartridges, and hence it is troublesome for users to replace the process cartridges.
In addition, the waste toner may escape from the waste-toner connecting part between the two process cartridges, and when the process cartridges are attached or detached, the procedure is designated, and hence usability deteriorates.
Moreover, since the apparatus has two types of process cartridges, twofold process cartridge insert guides and twofold cartridge fastener members are required. Hence, the whole electrophotographic apparatus becomes larger and the number of component parts increases, resulting in a high cost.
A large opening must be provided in order to attach or detach the two types of process cartridges, and the electrophotographic apparatus is so constructed that the whole front part thereof can be turned around to open. Hence, even though a damper mechanism is provided, this is a heavy-labor motion for users, and a large space and a high frame rigidity are required for such an opening-motion mechanism, resulting in a much higher cost. These are disadvantages of this type of apparatus.
Meanwhile, in Japanese Patent Applications Laid-open No. 11-30944 and No. 10-177329, a process cartridge is proposed in which a belt-shaped electrophotographic photosensitive member (photosensitive belt), an intermediate transfer belt and a waste-toner holder box are integrally constructed.
In the construction disclosed in these publications, the electrophotographic photosensitive member and the waste-toner holder box are disposed on the projection lower side of the intermediate transfer belt.
The apparatus is so constructed that, like the related art disclosed in Japanese Patent Application Laid-open No. 8-137181, a large movable-side frame can be turned around toward the front of the electrophotographic apparatus to open and the process cartridge in which the intermediate transfer belt, the electrophotographic photosensitive member and the waste-toner holder box are integrally held is inserted from the upper part.
The waste toner remaining on the intermediate transfer belt and the electrophotographic photosensitive member is scraped off with cleaning blades as cleaning means provided respectively for the two, and then collected in the waste-toner holder box.
The waste toner coming from the intermediate transfer belt drops downward from the upper part. This construction is not so complicated as the related art disclosed in Japanese Patent Application Laid-open No. 8-137181. However, like the related art disclosed in Japanese Patent Application Laid-open No. 8-137181, the waste toner is transported from the intermediate transfer belt and the waste toner is transported from the electrophotographic photosensitive member. Thus, the method for collecting the waste toner is troublesome and cumbersome, and besides, there still remains the risk that the toner may escape during transport.
An object of the present invention is to provide a novel process cartridge, an electrophotographic apparatus having such a process cartridge and an image-forming method making use of the electrophotographic apparatus, which have solved the problems the related art has had.
Stated specifically, an object of the present invention is to provide a novel process cartridge which can eliminate the user""s difficulty in replacing the process cartridge, can also prevent usability from being damaged by, e.g., the escape of waste toner from the waste-toner connecting part between the two process cartridges, can still also be kept from an increase in the cost and can further realize enhanced travel performance, durability, image quality and transfer performance of the intermediate transfer belt, and also provide an electrophotographic apparatus having such a process cartridge and an image-forming method making use of the electrophotographic apparatus.
More specifically, the present invention is a process cartridge which is detachably mountable on the main body of an electrophotographic apparatus; the process cartridge comprising the following integrally supported therein:
an electrophotographic photosensitive member for holding thereon a toner image;
an intermediate transfer belt having a contact zone coming into contact with the electrophotographic photosensitive member;
a primary-transfer means for primarily transferring the toner image from the electrophotographic photosensitive member to the intermediate transfer belt at the contact zone;
a charge-providing means for providing the toner on the intermediate transfer belt with electric charges having a polarity reverse to a polarity the toner has at the time of the primary transfer and returning the toner on the intermediate transfer belt to the electrophotographic photosensitive member at the contact zone to clean the intermediate transfer belt; and
an electrophotographic-photosensitive-member cleaning means for cleaning the electrophotographic photosensitive member;
the process cartridge being dividable into an electrophotographic photosensitive member unit having the electrophotographic photosensitive member and an intermediate transfer belt unit having the intermediate transfer belt, and having a joining means which joins the electrophotographic photosensitive member unit and the intermediate transfer belt unit together; and
the peripheral length L (mm) of the intermediate transfer belt, the average thickness t (mm) of the intermediate transfer belt and the diameter R (mm) of at least one of rollers over and around which the intermediate transfer belt is placed satisfying all the following expressions (1) to (4):
(1) 2xc3x97102xcfx80xe2x89xa6L/txe2x89xa64xc3x97104xcfx80;
(2) 2xc3x9710xe2x88x924xe2x89xa6t/Rxe2x89xa61.5xc3x9710xe2x88x922;
(3) 0.005 less than t less than 0.6; and
(4) 5 less than R less than 90.
The present invention is also an electrophotographic apparatus comprising:
an electrophotographic photosensitive member for holding thereon a toner image;
a charging means for electrostatically charging the electrophotographic photosensitive member;
an exposure means for forming an electrostatic latent image on the electrophotographic photosensitive member thus charged by the charging means;
a developing means for developing with toner the electrostatic latent image formed on the electrophotographic photosensitive member by the exposure means, to form a toner image on the electrophotographic photosensitive member;
an intermediate transfer belt having a contact zone coming into contact with the electrophotographic photosensitive member, through which the toner image is primarily transferred from the electrophotographic photosensitive member and thereafter the toner image having primarily been transferred is secondarily transferred to a transfer medium;
a primary-transfer means for primarily transferring the toner image from the electrophotographic photosensitive member to the intermediate transfer belt at the contact zone;
a charge-providing means for providing the toner on the intermediate transfer belt with electric charges having a polarity reverse to a polarity the toner has at the time of the primary transfer and returning the toner on the intermediate transfer belt to the electrophotographic photosensitive member at the contact zone to clean the intermediate transfer belt; and
an electrophotographic-photosensitive-member cleaning means for cleaning the electrophotographic photosensitive member;
the electrophotographic apparatus having a process cartridge in which the electrophotographic photosensitive member, the intermediate transfer belt, the primary-transfer means, the charge-providing means and the electrophotographic-photosensitive-member cleaning means at least are integrally supported and detachably mountable on the main body of the electrophotographic apparatus;
the process cartridge being dividable into an electrophotographic photosensitive member unit having the electrophotographic photosensitive member and an intermediate transfer belt unit having the intermediate transfer belt, and having a joining means which joins the electrophotographic photosensitive member unit and the intermediate transfer belt unit together; and
the peripheral length L (mm) of the intermediate transfer belt, the average thickness t (mm) of the intermediate transfer belt and the diameter R (mm) of at least one of rollers over and around which the intermediate transfer belt is placed satisfying all the following expressions (1) to (4):
(1) 2xc3x97102xcfx80xe2x89xa6L/txe2x89xa64xc3x97104xcfx80;
(2) 2xc3x9710xe2x88x924xe2x89xa6t/Rxe2x89xa61.5xc3x9710xe2x88x922;
(3) 0.005 less than t less than 0.6; and
(4) 5 less than R less than 90.
The present invention also relates to an image-forming method comprising:
a charging step of electrostatically charging an electrophotographic photosensitive member;
an exposure step of forming an electrostatic latent image on the electrophotographic photosensitive member thus charged in the charging step;
a developing step of developing with toner the electrostatic latent image formed on the electrophotographic photosensitive member in the exposure step, to form a toner image on the electrophotographic photosensitive member;
a primary-transfer step of primarily transferring the toner image formed in the developing step from the electrophotographic photosensitive member to an intermediate transfer belt by a primary-transfer means, the intermediate transfer belt having a contact zone coming into contact with the electrophotographic photosensitive member;
a secondary-transfer step for secondarily transferring to a transfer medium the toner image having primarily been transferred in the primary-transfer step;
a charge-providing step of providing the toner on the intermediate transfer belt with electric charges by a charge-providing means, the electric charges having a polarity reverse to a polarity the toner has at the time of the primary transfer;
an intermediate-transfer-belt cleaning step of returning the toner on the intermediate transfer belt to the electrophotographic photosensitive member at the contact zone to clean the intermediate transfer belt; and
an electrophotographic-photosensitive-member cleaning step of cleaning the electrophotographic photosensitive member with an electrophotographic-photosensitive-member cleaning means;
the image-forming method making use of an electrophotographic apparatus having a process cartridge in which the electrophotographic photosensitive member, the intermediate transfer belt, the primary-transfer means, the charge-providing means and the electrophotographic-photosensitive-member cleaning means at least are integrally supported and detachably mountable on the main body of the electrophotographic apparatus;
the process cartridge being dividable into an electrophotographic photosensitive member unit having the electrophotographic photosensitive member and an intermediate transfer belt unit having the intermediate transfer belt, and having a joining means which joins the electrophotographic photosensitive member unit and the intermediate transfer belt unit together; and
the peripheral length L (mm) of the intermediate transfer belt, the average thickness t (mm) of the intermediate transfer belt and the diameter R (mm) of at least one of rollers over and around which the intermediate transfer belt is placed satisfying all the following expressions (1) to (4):
(1) 2xc3x97102xcfx80L/txe2x89xa64xc3x97104xcfx80;
(2) 2xc3x9710xe2x88x924xe2x89xa6t/Rxe2x89xa61.5xc3x9710xe2x88x922;
(3) 0.005 less than t less than 0.6; and
(4) 5 less than R less than 90.
The above process cartridge, electrophotographic photosensitive member and image-forming method of the present invention, having the construction described above have the following advantages 1) to 5).
1) After taking the process cartridge for an electrophotographic apparatus out of the main body of the electrophotographic apparatus, users may divide the process cartridge thus taken out, into the electrophotographic photosensitive member unit and the intermediate transfer belt unit, and may replace only any unit having reached the end of its service life. Thus, some cost burden on users can be reduced.
2) On the side of manufacturers, too, there is an advantage that the matter can be dealt with by replacing only any defective unit.
3) A process cartridge can also be provided in which an intermediate transfer belt and an electrophotographic photosensitive member which are small-sized and low-cost are integrally supported, and hence the main body of the electrophotographic apparatus can also be small-sized. In addition, the opening for attaching or detaching the process cartridge can be set to be small and simple, so that the whole electrophotographic apparatus can be made low-cost.
As stated above, the process cartridge of the present invention employs a method in which the toner remaining on the intermediate transfer belt is returned to the electrophotographic photosensitive member at the contact zone between the intermediate transfer belt and the electrophotographic photosensitive member to clean the intermediate transfer belt (a cleaning-at-primary-transfer method or a bias cleaning method). As a means for charging the toner to a reverse polarity, which is necessary for such a cleaning method, a blade or a corona charging assembly may be used. Any means, however, may be used as long as electric charges can be applied to the toner remaining on the intermediate transfer belt without being transferred (transfer residual toner).
The transfer residual toner returned from the surface of the intermediate transfer belt to the electrophotographic photosensitive member is removed by an electrophotographic-photosensitive-member cleaning means such as a cleaning blade.
4) This bias cleaning method is greatly effective to make the process cartridge compact and low-cost, compared with a method in which cleaning blades or the like are provided for both the intermediate transfer belt and the electrophotographic photosensitive member and a feed mechanism for waste toner and a container therefor are installed.
Moreover, the intermediate transfer belt to be mounted on this process cartridge and be placed over and around rollers, and the rollers which transport and drive the intermediate transfer belt must not only show the above advantages but also contribute to good electrophotographic performances.
For example, large-diameter rollers are favorable for maintaining registration, but hinder miniaturization of the process cartridge.
The relationship between the intermediate transfer belt and the rollers may have an influence on the peripheral speed of the belt, and cause color misregistration when four-color toners are superimposed.
In addition, it is preferred that in general, the larger the peripheral length of the intermediate transfer belt, the thicker the belt. However, the thickness is limited in order to make the process cartridge compact. In particular, the thickness of the intermediate transfer belt may have a great influence on the value of a transfer electric field formed when the toner is transferred, and it can not easily be made large when the primary- and secondary-transfer performance of the intermediate transfer belt is taken into account.
5) Namely, where the peripheral length and average thickness of the intermediate transfer belt to be mounted on the process cartridge and the diameter of at least one of rollers over and around which the intermediate transfer belt is placed satisfy the above specific relationship, not only the above advantages, but also good electrophotographic performances can be exhibited.